perf(hash): reduce hash digest allocations

[intellild]

Summary

• replace hash salt storage with SmolStr
• avoid intermediate hash digest buffer copies before encoding
• encode base-N digests into SmolStr without String, to_vec, copy_from_slice, or reverse
• use inline SmolStr for short base-N output and write longer output directly into Arc<str> storage

Testing

• cargo fmt -p rspack_hash --check
• cargo test -p rspack_hash
• cargo check -p rspack_binding_api

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[github-actions]

📦 Binary Size-limit

Comparing 344794c to feat(css): add supports import, animation, customIdents, and dashedIdents for CSS (#14076) by AsyncIter

❌ Size increased by 4.00KB from 61.91MB to 61.91MB (⬆️0.01%)

[github-actions]

Rsdoctor Bundle Diff Analysis

⚠️ Note: The latest commit (a65509ae59) does not have baseline artifacts. Using commit 239535b63c for baseline comparison instead. If this seems incorrect, please wait a few minutes and try rerunning the workflow.

Found 6 projects in monorepo, 0 projects with changes.

📊 Quick Summary

Project	Total Size	Change
popular-libs	1.7 MB	0
react-10k	5.7 MB	0
react-1k	826.3 KB	0
react-5k	2.7 MB	0
rome	1.6 MB	0
ui-components	4.8 MB	0

Generated by Rsdoctor GitHub Action

[codspeed-hq]

Merging this PR will not alter performance

✅ 36 untouched benchmarks
⏩ 25 skipped benchmarks¹

---

_{Comparing codex/hash-smolstr-zero-copy (344794c) with main (239535b)}

Footnotes

1. 25 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩